The quality of material treated by roll mills, e.g. of seeds, such as grains or soybeans, depends upon uniform working conditions along the entire working surface or working line of the rollers pressed against one another. Especially in the case where there are no means to ensure a predetermined minimum gap between the rollers, damage might easily occur, if the rollers are pressed one against the other with elevated pressure without having particles between them. Mostly, flaking rollers are given a slight difference in rotational speed to "polish up" the flakes, so that lacking material between them, they would rub themselves and would damage their peripheral surfaces. But such damage or differences in wear may also occur due to a non-uniform supply of material to be milled. The worse the supply of material is in the lateral end regions of the rollers, the more they will be subjected to different wear in these end regions, as compared with the center regions. Such difference in wear is the reason, why it will become necessary too soon to regrind the rollers, this treatment causing long periods of disuse, because machining of the surfaces has to be done with particulaly high precision and, thus, with corresponding expenditures.
It has already been proposed (U.S. Pat. No. 3,282,199) to provide collecting structures at the lateral end regions of a roll mill, below the nip of the rollers, the collecting structure sealing the rollers by a wedge surface. Through tubings conveying the particulate material pneumatically, these collecting structures were connected to the feeder for refeeding the material to the rollers. Although it is possible to refeed the particulate material, which has emerged from the nip and is probably badly milled, with such a device, a relatively high energy consumption will result from the pneumatic conveyance and by refeeding through the feeder itself (which will be charged twice), on the one hand, whereas uniformity of wear and of feed is by no means ensured.
From German patent No. 29 00 922, a roll mill is known, the rollers of which having a reduced diameter in the lateral end regions. Collecting devices for material were provided on both ends, below the rollers, in order to refeed collected particles by a screw conveyor back into the feeder of the roll mill. Although the design with a reduced diameter of the roller ends may have a certain advantage, because it prevents a contact of the metallic peripheral surfaces in the critical end regions, the same disadvantages will occur as mentioned above.
U.S. Pat. No. 4,193,555 describes a roll mill, which is fed over a width slightly exceeding the length of the roller gap. On both sides of the gap, there are plate-like gap seals pressed against the flat front surfaces of the rollers. There is a small recess or groove provided in each of the gap seals for guiding the material better into the gap. These recesses extend just to the gap itself and may, thus, cause jamming of the material before the gap, because the (smaller) gap could not receive the particles. Accordingly, the recesses took more the shape of grooves in a relatively thin plate. Moreover, in practice, it was necessary, when separating the rollers from one another, to displace one end of one roller from the end of the other one, whereas the other roller has to be separated on its other end, so that their axes became inclined relatively to the normal operating position.